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Re: Air resistance



On 11 Dec 1997 08:49: Richard W. Tarara" <rtarara@saintmarys.edu> wrote:

All of the fussing over these data are precisely the reason I have stayed
away from 'automated' data acquisition and analysis in introductory labs.
While we can argue the fine points of averaging techniques, etc. here on the
list, ALL of this is totally opaque to students. For air resistance, I'll
stick with position versus time data, even if it has to be hand timed (our
experimental data for a 3 gr, 7cm diameter foam ball fits a v^2 dependence
quite well--certainly well enough to convey the main pedagogical thrust of
the designed experiment).

Before showing more data (see below) let me add another observation. The
rule which prevails in the lab should be that "data are bad only when
students do something incorrectly, otherwise they should be good". That
does not happen with "black boxes". During our experimentation we had to
reject data from numerous trials knowing very well that nothing was done
wrongly by us. Even in the case of coffee filters we often observed
strange curves and rejected them on the basis that "something is not
right" basis.

This is not very scientific. Styrofoam balls, which Dick Hodson has been
using for years, are much better from the pedagogical standpoint. In any
case, I am showing the falling coffee filter data from one of our good-
looking set, T8. Again the sampling rate was 40 per second and averaging
was 15. The total mass (3 filters and Al disk) was 13 grams; no significant
buoyancy complication in this case. Please analyse the data "your way" and
find the "best fit" values of b and n (assuming R=b*v^n), where R is the
air resistance force.

The first and the last data points are certainly inside the good data region,
as defined by John Gastineau (yesterday). What is the range of acceptable n
values?

t(s) d(m) v(m/s) a(m/s^2) R(N)

1.050 0.714 1.506 4.34
1.075 0.757
1.100 0.800
1.125 0.845
1.150 0.883
1.175 0.927
1.200 0.987
1.225 1.045
1.250 1.103
1.275 1.165
1.300 1.229
1.325 1.306
1.350 1.364
1.375 1.430
1.400 1.500
1.425 1.591
1.450 1.677
1.475 1.744 3.117 1.73